# Winter moth (Operophtera brumata) > A small geometrid moth whose flighted males and nearly wingless females appear in late autumn; larvae are spring leaf-eating caterpillars and can be major tree pests. Source: https://insectscanner.com/species/winter-moth/ (updated 2026-10-10) ## Is it dangerous? **Non-toxic.** Winter moths and their caterpillars are not venomous and do not bite or sting. The caterpillars are smooth and hairless and are harmless to handle; wash hands afterwards as a routine precaution. **Pets:** Larvae may be eaten by pets; a few caterpillars are unlikely to cause serious harm, but large amounts could cause gastrointestinal upset. If a pet shows persistent vomiting, lethargy or other concerning signs, consult a veterinarian. ## Quick facts - Scientific name: Operophtera brumata - Order: Lepidoptera (Moths and butterflies) - Family: Geometridae (Geometer moths) - Size: Males 22-28 mm wingspan; females flightless with tiny stubby wings - Colours: Mottled brown, Grey, Green, Cream, Black - Habitat: Deciduous and mixed woodlands, orchards, gardens and urban trees; eggs and adults found on tree trunks and branches - Range: Native to Europe; introduced and established in parts of eastern and western North America and other regions - Active: Adults fly in late autumn to early winter (often November to January); larvae feed in spring (March to May) - Lifespan: Adults live a few weeks (short-lived); full generation cycle is annual - Effect on plants: Defoliator - Pest: yes ## Overview The winter moth is a small geometrid moth notable for its unusual seasonal activity and strong sexual dimorphism. Adults are active in late autumn and early winter when few other moths fly; males are slender and winged while females are almost wingless and climb trees to mate and lay eggs. Eggs overwinter on bark and hatch in early spring; the green larvae feed on leaves of many deciduous trees and shrubs and can cause heavy defoliation in outbreak years. Native to Europe, the species has become established and invasive in parts of North America. ## How to identify it Adult males have narrow, mottled brown-grey wings and a slim body; wingspan typically about 22-28 mm. Females are nearly wingless or have greatly reduced wings and a plump, grey-brown body adapted for crawling rather than flying. Caterpillars are green with a faint white or pale stripe along the back, slender and inchworm-like, reaching about 20-25 mm at full size. - Late-autumn to winter flight: small brown, narrow-winged moths flying on mild winter nights (males). - Strong sexual dimorphism: males winged and mottled brown-grey; females largely wingless and crawl on trunks. - Spring caterpillars are small green inchworms with a faint pale dorsal stripe, seen on buds and new leaves. - Eggs are tiny, laid singly or in small groups in bark crevices and under lichen; look for them on trunks and twigs in winter. ## Lookalikes - **Bruce spanworm** (Operophtera bruceata): Very similar appearance and biology; separation often requires range, subtle wing-pattern differences or dissection/genitalia examination. In North America, both species may co-occur. - **Autumnal moth** (Epirrita autumnata): Autumnal moth adults fly earlier in autumn and have different wing markings and flight period; larvae and damage timing differ. - **Mottled umber** (Erannis defoliaria): Another geometrid with flight in cooler months; check wing pattern, flight timing and female wing development (species differ in female wing size) to distinguish. ## Life cycle - **Egg:** Laid by females on bark and in crevices in late autumn to early winter; eggs overwinter and hatch in early spring around budbreak. - **Larva (caterpillar):** Green inchworm-like caterpillars feed on expanding leaves and flowers in spring; this is the main damaging stage and lasts several weeks. - **Pupa:** Mature larvae drop to the soil in late spring and pupate in the litter or shallow soil; pupal stage lasts through summer and autumn. - **Adult:** Adults emerge in late autumn to early winter to mate; males fly while females are mostly wingless and climb trees to lay eggs. ## Diet and predators - Young eat: Young leaves and flower buds of many deciduous trees and shrubs (oak, maple, apple, beech, hawthorn, cherry, etc.) - Adults eat: Adults do not feed appreciably; they are short-lived and focused on mating and egg-laying. - Predators of the young: Birds, predatory insects and spiders; some parasitic wasps and flies attack larvae - Predators of adults: Insectivorous birds and some bats (males); ground predators may take flightless females ## Effect on plants and gardens Larvae feed on the leaves of many deciduous trees and shrubs, including oak, maple, apple, beech, hawthorn and cherry. Heavy infestations can cause significant defoliation, reduced growth, and increased susceptibility to other pests and diseases. ### How to get rid of it Use a combination of monitoring and timed controls. Sticky bands on trunks in late autumn and early winter catch crawling females and reduce egg laying. Pheromone traps monitor male activity to time interventions. Apply Bacillus thuringiensis kurstaki (Btk) sprays in early spring when larvae are very small (typically just after budbreak) for effective biological control. In some invaded regions, a parasitic tachinid fly (Cyzenis albicans) has been used as a biological control agent; such releases are done by authorities. For isolated trees, hand removal of egg masses in winter and pruning dense twig areas can help. Avoid broad-spectrum insecticides where possible to protect native predators and parasitoids. ## Where and when to find it Adults: on tree trunks, branches and near lights on mild late-autumn nights. Females crawl on trunks. Eggs: on bark crevices and twigs in winter. Larvae: on buds and newly expanded leaves of deciduous trees in spring. - Best time: Adults: November to January (mild nights). Larvae: March to May. Best time of day: crepuscular and night for males, daytime for finding females on trunks or larvae on leaves. - Tips: Use a flashlight on mild winter evenings to spot flying males. Wrap a sticky band around trunks in late autumn to catch wingless females. In spring, inspect tree buds and new leaves early in the morning for small green inchworms. ## Fun facts - Winter moth adults fly when most other moths are inactive, often on mild nights in late autumn and early winter. - Females are almost wingless and must climb tree trunks to mate and lay eggs — an unusual trait among moths. - Introduced populations in North America have caused major tree defoliation events and spurred biological control programs. ## Frequently asked questions ### Are winter moths dangerous? No. They are not venomous or harmful to humans, though their caterpillars can cause defoliation of trees. ### Do winter moth caterpillars bite or sting? No. The caterpillars are smooth, hairless inchworms that do not bite or sting and are harmless to handle. ### Why are winter moths in my house? Males may be attracted to lights on mild winter nights and can come into houses through open doors or windows. Females do not fly far but may crawl onto buildings when seeking trees to climb. ### How do I get rid of winter moths in my trees? Monitor with pheromone traps to time control. Place sticky bands on trunks in late autumn to trap females. Apply Btk sprays in early spring when larvae are very small, and remove egg masses by hand in winter. For large outbreaks, contact local extension or forest health authorities about biological control options. ### Where do winter moths live? They are native to Europe and found in woodlands, orchards, hedgerows and urban trees. Introduced populations occur in parts of North America where they inhabit similar environments. ### When should I look for or expect damage? Eggs are visible on bark in winter; larvae feed and cause leaf damage in spring around budbreak (typically March to May depending on latitude). --- More about this species: [iNaturalist](https://www.inaturalist.org/taxa/60780), [Wikipedia](https://en.wikipedia.org/wiki/Winter_moth). Identify insects and spiders from a photo with the Insect Scanner iPhone app: https://apps.apple.com/app/id1543946563?pt=126685406&ct=web-markdown&mt=8 Identification from photos is never certain: don't handle insects you can't identify, and get medical advice for bites, stings or allergic reactions.